1. Field of the Invention
The present invention concerns a CT-assisted or MRT-assisted image acquisition, image archiving and image rendering system for generation, storage, post-processing, retrieval and graphical visualization of computed or magnetic resonance tomography image data that, for example, can be used in the clinical field in the framework of radiological slice image diagnostics as well as in the framework of interventional radiology. The present invention also concerns a method implemented by such a system for reproduction of patient-specific examination parameters of an initial examination implemented by means of computer or magnetic resonance tomography imaging in the framework of CT or MRT follow-up examinations (“follow-ups”), for example in a post-operative tumor examination implemented under slice image monitoring in connection with a histological tissue sample extraction (biopsy) implemented under local anesthesia or a minimally-invasive intervention implemented for tumor treatment.
2. Description of the Prior Art
In the case of certain clinical situations, in particular in the field of tumor diseases, today monitoring examinations (“check-ups”) are implemented at predetermined time intervals by means of slice image diagnostics. In particular modern radiological imaging methods such as, for example, computed tomography (CT), positron emission tomography (PET) in combination with computer tomography or magnetic resonance tomography (MRT) are used. By means of these regularly conducted check-ups it is possible to register changes of the clinical picture of a patient that are externally not visible. In the event that the cancer reappears in a tumor patient or a new, malignant tumor develops from metastases, these can be promptly detected and be operatively treated as quickly as possible using a minimally-invasive procedure or conducted under local anesthesia. If the medically recommended post-operative tumor examinations are consistently administered by the patient and the indicated therapies are conducted, in many cases a cure, life extension or at least maintenance of the quality of life are real possibilities.
A predetermined standard examination protocol is typically loaded to plan the initial examination, in which standard examination protocol examination, acquisition and 2D/3D image rendering parameters (reconstruction parameters) are then manually adapted by a radiologist conducting the examination to a patient to be examined by means of CT, PET-CT or MRT.
In order to be able to compare image data of an initial examination implemented by means of CT-, PET-CT- or MRT-assisted imaging (which image data are presented in the form of axial slice exposures or in the form of reconstructed 2D projections or 3D views of areas to be examined inside the body of a patient) with those of subsequent monitoring examinations of the patient (likewise conducted under CT or MRT imaging) as well as possible, in the ideal case the same acquisition parameters as in the initial examination should be used in the follow-up examinations. Moreover, the slice exposures displayed on the screen, reconstructed 2D projections or 3D views of tissue regions, organs, anatomical subjects or pathological structures that are to be examined (such as tumors, metastases, hematomas, abscesses etc., for example) inside the body of the patient should be reconstructed with the same 2D or 3D reconstruction parameters as in the initial examination. Conventionally, all parameters from the initial examination must be input manually into the CT or MRT system by a radiologist conducting the initial and follow-up examination.
Since in present-day radiological imaging, image archiving and image processing systems it is not possible to store all parameters that were set in an initial examination of a patient implemented by means of CT, PET-CT or MRT, at present there exists no possibility to precisely set these parameters again in subsequent CT-, PET-CT- or MRT-based follow-up examinations so that the examination results of the radiological initial examination can be exactly reproduced. For the same reasons deviations between the image data of this initial examination and the image data of a radiological follow-up examination that show an improvement or worsening of a pathological state diagnosed in the framework of the initial examination cannot be evaluated under the same acquisition and reconstruction conditions.
A further problem of present CT-assisted or MRT-assisted imaging, image archiving and image processing systems is that the position occupied by a patient on the examination table of a CT or MRT apparatus (i.e. the patient position) in an initial examination cannot be exactly repeated upon implementation of a follow-up examination, i.e. with the same position and angle coordinates relative to a three-dimensional Cartesian coordinate system I (patient coordinate system) which is spanned by the longitudinal axis z of the body of the patient and two direction vectors proceeding orthogonal to one another in the x-direction (transverse-horizontal) or in the y-direction (transverse-vertical). These direction vectors are direction vectors of a slice plane Exy normal (transverse) relative to the longitudinal axis of the body, with a suitably established point A indicating the position of the coordinate origin in the patient coordinate system. This leads to the situation that two different inertial systems I and I′ must be differentiated, i.e. a three-dimensional Cartesian coordinate system I′ defined by the spatial position of an examination table movable relative to the CT or MRT apparatus in the feed direction z, with a coordinate origin O′ as well as three axes x′, y′ and z′ orthogonal to one another (table coordinate system), and the patient coordinate system I defined by the position of the patient relative to this table coordinate system, with a coordinate origin O as well as the three aforementioned axes x, y and z orthogonal to one another. If the patient lies prone on the examination table of the CT or MRT apparatus, the y-axis of the patient coordinate system and the y′-axis of the table coordinate system are parallel to one another and the planes spanned by the x-axis and z-axis of the patient coordinate system, and by the x′-axis and z′-axis of the table coordinate system, are coplanar with one another. Since, upon implementation of a CT or MRT examination, the patient is not always able to exactly occupy the same orientation and position as in a prior examination implemented by means of computed tomography or magnetic resonance tomography imaging (even with repeated correction of his or her resting position occurring at the instruction of a radiologist in advance of the radiological examination), it must be noted that the position offset and angle offset coordinates (which are required for an initial CT-assisted or MRT-assisted examination in order to convert between both coordinate systems) are generally not correlated with the corresponding position offset and angle offset coordinates in subsequent examinations conducted in the framework of computed tomography or magnetic resonance tomography imaging processes. For this reason, all position and angle coordinates that are used to define the x-, y- and z-positions and the orientation in the φ-direction and the or θ-direction of a 2D or 3D reconstruction generated in the framework of a 2D or 3D post-processing by means of multiplanar reformation, maximum intensity projection or volume rendering technique, are always related to the table coordinate system. However, all of these position and angle coordinates must actually relate to the patient coordinate system in order to be able to achieve exactly reproducible image data independent of the patient position in temporally successive examinations.
Since a repetition of the CT-assisted or MRT-assisted imaging process under the same conditions as in an initial examination (with the exact same parameter specifications) of the appertaining patient implemented by means of CT or MRT is presently not possible upon implementation of a radiological follow-up examination, both examinations are typically planned and implemented individually. The parameter settings for the radiological follow-up examination are reestablished starting from the image data generated in the framework of the initial examination and are used for generation of 2D or 3D reconstructions and protocolled data of a scan protocol acquired after conclusion of the scan procedure of this initial examination and stored in a report or, respectively, finding file. This is a relatively time-consuming process that must be manually executed by a radiologist implementing both examinations.
In the planning of the follow-up examination it should be noted that the standard examination protocol used in the framework of the initial examination must be reused, and all information displayed in graphical or text form on the display screen of a monitor terminal connected with the CT or MRT system (which information relate to the setting parameters of the initial examination), such as the acquisition and reconstruction parameters displayed in a display window in the form of image text, for example, must be checked and possibly reconfigured.
Moreover, the spatial orientation of the slices shown in an initial examination in the framework of an MRT-assisted imaging process, nor the spatial orientation of 2D or 3D reconstructions that were generated in the framework of a post-processing process implemented after the initial examination, are not reproducible in commercially available CT and MRT systems. Rather, such information must be estimated on the basis of the respective prior examination and be manually input by the radiologist conducting the examinations, which (apart from the not inconsiderable time expenditure that accumulates over multiple follow-up examinations) is prone to a relatively large imprecision of the image reproduction.
Added to this is the imprecision (described above) ascribed to the non-correlation of the respective position offset and angle offset coordinates of table coordinate system and patient coordinate system in temporally successive CT-assisted or MRT-assisted examinations that have been conducted with different patient positions. The position offset coordinates (Δx, Δy and Δz) and/or the angle offset coordinates (Δφ) with which the two inertial systems I and I′ can be converted into one another before implementation of the initial examination, and the corresponding offset coordinates with which the table coordinate system and the patient coordinate system can be brought into relation to one another in advance of a follow-up examination, can be only conditionally approximated to one another (i.e. brought into correlation with one another). For example, this can occur when the patient is lying in extended dorsal, prone or side position on the examination table of a CT or MRT apparatus, and is instructed to change his/her recumbent position until he/she comes to lie with a punctiform spot P(x0, y0, z0) on his/her body surface (for example at a specific point in the cranial region of the calvaria) exactly on an established punctiform spot P′(x0′, y0′, z0′) on the top of the examination table. This leads to the situation that the position offset and angle offset coordinates in the respective follow-up examination exhibit the same values as in the initial examination. For this purpose it is required that the appertaining body point P be detected with the use of a laser sighting device in each examination before implementation of a scan process, and the table position is recalibrated so that the two aforementioned punctiform spots P and P′ come into congruence. By suitable establishment of the positions of these two punctiform spots and consolidation of the direction of the table feed (axial direction) with the z-axis of the patient coordinate system it can also be ensured that the table and patient coordinate systems coincide. This method is naturally very strongly dependent on how precisely the radiologist conducting the examinations sets the position of the examination table. A subsequent correction of the table position given a position change of the patient by Δx and/or Δz in the ±x-direction and ±z-direction (i.e. in the transverse-horizontal and axial directions) or given a rotation of his/her position by Δφ in the ±φ-direction (i.e. via rotation on an axis perpendicular to the x-z-plane of the patient coordinate system, which x-z-plane is parallel to the table plate plane) is not possible during the implementation of a CT, PET-CT or MRT scan process.